Voltage regulator



May 16, 1944.

w. c. GRABAU VOLTAGE REGULATOR Filed Sept. 17, 1940 '0 EXCITER RHE TAT. J 0S INVENTOB. M/IY/I'OM (his/I44 mbao BY 14mm ZATTORNEY i' Patented May 16, 194 2- UNITED STATES PATENT OFFICE VOLTAGE nacuui'roa William Christian Grabau, Boston, m, assignor to Submarine Signal Company, Boston, Mass., a corporation of Maine Application September 17, 1940, Serial No. 357,132

4 Claims.

The present invention relates to an electrical circuit and apparatus for regulating and controlling an alternating current line voltage between .wide voltage variations.

the purpose of maintaining constant line voltage in both systems.

In the ordinary 110 volt alternating current supply system it is desired to maintain the voltage constant at 110 volts for all loads and in particular it is desirable to avoid fluctuations or changes in voltage with fluctuations in load.

In the present invention the desired alternating current voltages may be maintained at its predetermined value as, for instance, 110 volts without fluctuations, hunting or overshooting which otherwise frequently occurs. In the present system a separate exciter may be employed with a rheostat in the exciter field which is continually being connected out and into the field circuit in such a way as to vary the exciter field current and thereby vary the delivered exciter voltage and the main generator field.

In the present invention the alternating current voltage regulation is maintained constant through variation in the control circuit both of the applied exciter voltage and the rectified component oi the voltage obtained from the alternating source whose voltage is to be controlled. The circuit and apparatus in the present case are particularly applicable to control by means of a current transformer in which, oi. course, the potential generated in the circuit connected with the current transformer is dependent upon the load in the generator circuit rather than upon alternating and direct current supply the voltage across the system. With increasing load, therefore, the component of voltage associated with the load increases and this is compensated by the component applied from the direct current exciter source. The system in the present case permits the use of a rising voltage characteristic with increasing load which in itself has -a useful application for a power line supply circuit where the load may be at a distance from t the power source.

Other features and advantages of the present invention will be understood from the following description given below and taken in connection with the drawing showing an embodiment of the invention in which Fig. -1 shows the circuit armachine, the flux for which is supplied by the v field coil 2 energized by means of a direct current exciter 3 which may be driven on the same shaft as the alternating current generator I, which direct current exciter supplies direct current field excitation for the field winding 2. current -exciter also furnishes a direct current supply for the direct current terminals 4 which are used in the control system. The .exciter direct current generator is preferably self-excited through the exciter field 5 which has in series connection the exciter field rheostat 6, which elements 5 and 6 are connected in series across the exciterterminals. In the control system which will presently be described the exciter field resistonce 6 is cut in and out of circuit by shorting or opening the terminal conductors l and 8 connected across the exciter resistance. When'the resistance 5 is in circuit with the field 5 across the exciter terminals, the field strength is decreased because of the added resistance in the field circuit. This decrease in the field decreases the voltage generated by'the excites which therefore lowers the direct current voltage across the supply 4 and also lowers the current flowing in the generator held 2 and therefore the terminal voltage across the alternating current generator. On the other hand, when the exciter resistance is shorted by shorting the connection across the terminal lines i and 8, 'the'fielcl current 5 is increased with the-result that the direct current exciter voltage across the supply at l is increased as well as the current in the field coil 2 and therefore the voltage across the terminals of the generator I.

The shorting of the terminal conductors l and 8 is controlled by means of the relay switch con,-

tacts 8 of the relay I0. when the contacts 9 are closed, the circuit across the terminals l and 8 is closed, with the result that the voltage delivered by the generator i will increase, and, on the other hand, when the terminals 9 are opened, the reverse will happen, that is the voltage across the'generator i will decrease. The alternatin current supply voltage is controlled by means of the exciter and exclter circuit, Just described, in connection with the vacuum tube circuit control which will now be described.

The vacuum tube control circuit includes a vacuum tube II with cathode l2, anode i3 and control grid I4 and a second vacuum tube IS The direct havlngacathodeli,andanodellandagridll. Thegridllottheiirstvacuumtubeisconnected throughapotenflometerorslidewlredropila hill bitter! II anda second or slidewiredrop liwhichitselliaconnectedacrossthedirectcurrentsupplyl. Asindicatcdbythe anownthepotentlometerll suppliesaposidve potentialtothegridllwithrespecttofllecathcomes directly from the alternating current supply line 23 by means oi the current transformer 24. As the load through the line 23 is increased,

the voltage delivered by the transformer II is increased and thereby a greater potential is impressed through the coupling transformer 2" across the potentiometer ll in such a direction astolncreasethebiasonthegrid lloithetube ll. When the grid ll of the tube ii becomes more negative, the plate current in the tube Ii decreases, decreasing the bias oi the grid II in the tube It with respect to the cathode It.

In this way the plate current in the tube Ii is increased, increasing the current flow in the winding 2. of the relay 21 which brings aboyt an operation of the relay 21 which is acontrol relay for controlling the power relay it, the operation of which shorts the r or resistance 0 in the exciter field. Therefore, as the load through the line 28 increases initially, the rheostatorresistanceiin theexciterfleldiscut out of circuit, thereby permitting the exciter terminal volts to increase and also the current through the generator ileld 2 and the terminal alternating current voltage acrossthe generator I. It will be noted, however, that the increase of theexcitervoltageacrosstheterminalslisin aichadireetionastodecreasethe-negativebias iromthecathodetogridoithetube ll,thereby restoringthegrid lltoitsnormalloadcondition.

Inthearrangemmtwhichhasjustbemde- :scrlbedJtwillbenotedthatanincreaseinalwithintheoperatingvoltsgeoithesystemand" in fact this regulation iscontrollable ior avoltage rangeotatleasttwotothreetimesthelowest voltage. It should be noted in the circuit Just described that the alternating current source provided across the secondary oi the tr-stormer' liisrectitledbymeansoitherectiflerlltopmduce a pulsating rectified potential across the potentiometer ll.

Initially the tap i2 is adjusted to producethe desired alternating current potential for no-load operating condition. To maintain the same voltageastheioadincreaseaassumingthatthegelb erator speed remains constant, the iield 1 must increase in proportion to the increase in load. Thisincrease inthe field I isbroughtabout by the increase in the direct current excite! voltage relatedtothelncreaseinload. Inthiawaythe increaseinexcitervoltageandtheincreasein theiieldcurrentintheiieldlkeepstepwiththe .increaseinthealternatingcurrentload. when theloadinthelineadromthencorrespondinglythcdirectcurrentexcitesvoltagedecreases. decreasingtheiieldltoprovidetheduiredregulated voltageacrossthe generator terminals.

In theregulI-tion from no load to full load proper choice of the various elements inthecir- L cuit. Regulation at no-load condition is obtainedentirelythroughthedirectcurrentsmarce lbymeansoiwhichthegrldlli'scontrollett' Thevoltage iorthepotentiometerll mayaho beobtainediromatransiormerconnectedacro. thelineorsomepotentialdevice. Inthiscan thepotentialinthepotentiometerlidoesnot increasewithcurrentbutonlywithvoltagevarlationssothattheincreaseotexcitationinthe iieldlcallediorbyfullloadoverno-loadconditions must be opposed by a greater-riseinthevoltsgeacrosstheline. To thisextentthearrangementshownhasapsei'erableadvantage. v

Inl'ig.2thevaflationotthedirectcurrmt exciter fleld to maintain constant alternatim current voltage conditions is obtained by means ota'variablereactanceintheexcitu'ileldcircuit. Inthiscasetheplatelloi' whlchmaybethesame circuit-theprimaryll of actancellthesecondaryllofwhichisin seriescirouitwiththeercita'iieldlLthei'ecflfleruandthealterhatingcurrentmachinc whichistobemm Asthecurrentintheplatecirmitoitbe liincreaseatheinductanoepresentedbyu theflelddrcuitdecreasesandpermitsmorecurrenttoilowinthefleldcircuituJhusinueasoitheplatecurrentinthetubellworkslnthe oppositedirectiontolomthealternatingcurrentvoltage.".lheshowninflg.l eliminates the relay action and provides field cun'entchangesintheiormoiacontinuouscurve withoutpointshav'ingindeterminateslopa.

Havingnowdescribedmyinventiom-Iclaim: hasystemrorregulatingthevoltageundes loadoperation oianalternating currentlnacbine havingaiieldwindingandadirectcurrentuciteriorenergiaingsaidfleldwindingacircuit havingaiieldwindingiorsaidexciterandconnectedacromsaidexcitenmansiorvlrllnlflle currentinsaideacit'eriieldwindingdreuitin eluding a vacuum tube control circuit having an initialcontroltubewithcatlsodeanodeandgrid controlelectrodeaandasecondconisoltube having anoutput circuit with the cathodeand anodctbereolenergisedbysaidexcitermems i'or applying to'said grtd control electrodes 9! gamma said vacuum tube control circuit in series opposing relationship, potentials relating to the terminal exciter voltage and rectified potentials proportional to the alternating current load, relay means operatively connected in the output of said vacuum tube control circuit for shorting in and out a portion of the impedance in said exciter field winding circuit, whereby the current therein varies and voltage regulation is-obtained.

2. A system for regulating the voltage under load operation of an alternating current machine having a field winding and a direct current exciter for energizing said field winding, a circuit having a field winding for said exciter and connected across szid exciter, means for varying the current in said exciter field winding circuit including a vacuum tube control circuit having an initial control tube with cathode, anode and grid control electrodes, and a second control tube having an output circuit with the cathode and anode thereof energized by said exciter means for applying to said grid control electrodes of trol electrodes, the anode-cathode circuit of said second tube being energized by said exciter,

being operatively connected together whereby an increase of the. negative bias on the grid of the first tube will cause an increase in the anodecathode current of the second tube and a decrease in negative bias of the grid of the first tube will cause a decrease in the anode-cathode current of the second tube, and relay means operatively connected in the plate circuit of the said vacuum tube control circuit in series opposing relationship, potentials relating to the.terminal exciter voltage and rectified potentials proportional to the alternating current load, a relay having its operating coil connected in the output of said vacuum tube control circuit and a second relay operated by said first relay for shorting in and out part of the impedance in said exciter field winding circuit, whereby the current therein varies and regulation of the alternating current generator is obtained.

3. A system for regulating the voltage under load operation of an alternating current machine having a field winding and a direct current exciter tor energizing said-field winding, a circuit having a field winding for said exciter and connected across said exciter, means for varying the current in said exciter field winding circuit including a vacuum tube control circuit having a pair or vacuum tubes, designated ,as first and second tubes, including anode, cathode and consecond tube for shorting in and out an impedance in the field winding circuit of said exciter where by the current therein varies and the alternating current voltage is regulated.

4. A system for regulating the voltage under load operation having an alternating current machine having a field winding and a direct current exciter for energizing said field winding, a circuit having a field winding for said exciter and connected across said exciter, means for varying the current in said exclter field-winding circuit including a vacuum tube control circuit having an initial control tube with cathode, anode and grid control electrodes and a second control tube including anode, cathode and control grid electrodes having an output circuit with the cathode and anode thereof energized by said exciter, means for applying to said grid control electrodes 01 said vacuum tube control circuit in series opposing relationships, potentials relating to the terminal excitervoltage and rectified potentials proportional to the alternating current load, and means operative through the output of said second vacuum tube for varying the impedance in said exciter field winding circuit whereby the current therein varies.

lWILLIAM cnars'nm GRABAU. 

